1. Field of the Invention
The invention concerns a pump and a valve unit for a pump. The invention in particular concerns a vacuum pump or a compressor, respectively, and a non-return valve unit for a vacuum pump or a compressor, respectively, of this type.
2. Background Art
As it is known, pumps of this type may be used for delivery of fluids. In this disclosure, the term fluid refers to a medium such as a liquid, a gas or a liquid-gas mixture. Non-return valves are conventionally arranged on the suction side of pumps in order to prevent a backflow of fluid after switching off the pump. The arrangement of the non-return valves in a vacuum pump poses the problem that there is merely an extremely low pressure on the suction side of the pump. While the non-return valves should on the one hand provide reliable sealing, they should on the other hand have no pressure loss at all or only to a very low extent. Even minute amounts of pressure loss already reduce the attainable ultimate vacuum of the vacuum pump.
Vacuum pumps are often equipped with spring-loaded non-return valves. The springs used therein should have a low spring stiffness for the non-return valves to open easily in the event of a particular flow while causing only a minor amount of pressure loss. After switching off the pump, the spring should press the valve disk against the valve seat in a light but sealing manner. Process-safe fabrication of springs having these properties is however very difficult.